In many medical situations, the pulmonary functions (i.e., relating to the lungs) of a patient need to be monitored, controlled or accessed, and in many circumstances for days at a time. To achieve this, the medical field often uses a respiratory circuit which is connected to a ventilator, which is sometimes referred to as a respirator. Typically, respiratory circuits include a breathing tube (e.g. endotracheal tubes, tracheostomy tubes, laryngeal mask airways, and the like) that acts as the interface between the patient and the respiratory circuit. For instance, an endotracheal tube is inserted through the mouth or nasal passages of the patient and into the trachea. Usually, a balloon or cuff surrounding the inserted end of the tube is inflated to provide a seal between the endotracheal tube and the trachea. Once sealed, the patient breathes through the endotracheal tube.
Once a breathing tube is connected to a patient, other components of the respiratory circuit are coupled to the breathing tube. Usually, a ventilator tube links the breathing tube with a ventilator which monitors, and if necessary can control, the pulmonary functions of the patient. Other components, such as junctions, moisture traps, filters, humidifiers and the like, optionally can be added to the respiratory circuit. For instance, drug delivery systems can be added to the respiratory circuit to delivery aerosolized medicine to the lungs of the patient. In some circumstances, medical care givers require access to the lungs and/or trachea of the patient. For example, suction catheters are used to remove secretions in a patient's lungs. In such circumstances, special junctions can be added to the respiratory circuit which allow such access without interrupting the monitoring or control of the pulmonary functions.
An ongoing challenge with respiratory circuits is maintaining a sterile environment. Indeed, one clinical study has concluded that "trying to maintain a sterile ventilator circuit for 24 hours is a difficult and perhaps impossible task." Contaminated Condensate in Mechanical Ventilator Circuits, Donald E. Craven, et al., Concise Clinical Study, p. 627. Due to the inherent moisture and warmth, respiratory circuits provide superb conditions for microbiological growth or colonization. Once colonization has started, the microbiological growth can easily spread to the patient, either airborne or through moisture condensation running down into the patient's lungs, thus risking infections and complications, often resulting in pneumonia.
The problem of respiratory circuit colonization is especially prevalent within breathing tubes. For instance, studies has documented the health risks from colonization in endotracheal tubes, sometimes called a biofilm, which can be so extensive that the walls of the endotracheal tube become slimy and sticky. See Nosocomial pulmonary infection: Possible etiologic significance of bacterial adhesion to endotracheal tubes, Frank D. Sottile et al., Critical Care Medicine, Vol. 14, No. 4, p. 265. Due to the close proximity to the patient's lungs, any microbiological growth in a breathing tube can easily spread to the patient's lungs. Condensed moisture can run down the breathing tube, over the biofilm and into the patient's lungs. Additionally, chunks of the biofilm can actually fall off the breathing tube and into the patient's lungs.